Water-absorbent film construction

ABSTRACT

This invention relates to a water-absorbent film construction, comprising: a water-absorbent film layer overlying a base layer, the water-absorbent film layer being comprised of at least about 40% by weight of at least one 2-oxazoline polymer.

TECHNICAL FIELD

[0001] This invention relates to water-absorbent film constructions.More particularly, this invention relates to a water-absorbent filmconstruction comprising a water-absorbent film layer overlying a baselayer, the water-absorbent film layer being comprised of at least about40% by weight of a 2-oxazoline polymer.

BACKGROUND OF THE INVENTION

[0002] Polymers of 2-oxazolines are known to be hydrophilicwater-soluble materials. These polymers have utility as adhesionpromoters and viscosity modifiers. Unfortunately, however, thesepolymers when formed into solid articles such as films exhibit poormechanical properties. For example, dried films of 2-oxazoline polymersare too brittle to be useful in many applications and water often causesdissolution of such films.

[0003] Despite mechanical problems which limit the utility of thesepolymers, 2-oxazoline polymers have many desirable properties and itwould be advantageous if they could be utilized in a film construction.The problem therefore is to pprovide a film construction containing a2-oxazoline polymer that takes advantage of the desirable properties ofthis polymer and yet exhibits sufficient mechanical and physicalproperties to be of practical use. This problem has been overcome withthe present invention.

[0004] U.S. Pat. No. 4,678,833 discloses miscible blends ofpoly-2-oxazolines and thermoplastic polymers. These blends are describedas being useful as membranes for separating components of liquidmixtures such as water/ethanol or ethanol/hexane mixtures.

SUMMARY OF THE INVENTION

[0005] This invention relates to a water-absorbent film construction,comprising: a water-absorbent film layer overlying a base layer, thewater-absorbent film layer being comprised of at least about 40% byweight of at least one 2-oxazoline polymer.

[0006] In one embodiment of the invention, the base layer has a firstside and a second side, the water-absorbent film layer overlies thefirst side, and a skin layer overlies the second side.

[0007] In one embodiment of the invention, the inventive filmconstruction further comprises a tie layer positioned between thewater-absorbent film layer and the base layer.

[0008] In one embodiment of the invention, the base layer has a firstside and a second side, the water-absorbent film layer overlies thefirst side, a tie layer is positioned between the water-absorbent filmlayer and the base layer, and a skin layer overlies the second side.

[0009] In one embodiment of the invention, the base layer has a firstside and a second side, the water-absorbent film layer overlies thefirst side, a skin layer overlies the second side, and an adhesive layeroverlies the skin layer. In one embodiment, the adhesive layer iscomprised of a pressure sensitive adhesive, and a release liner overliesthe pressure sensitive adhesive.

[0010] In one embodiment, the invention relates to a water-absorbentfilm construction, comprising: a water-absorbent film layer having a2-oxazoline polymer concentration of at least about 40% by weight; abase layer, the base layer having a first side and a second side, thewater-absorbent film layer overlying the first side of the base layer;and a skin layer comprising at least one heat-activatable adhesivematerial overlying the second side of the base layer.

[0011] In one embodiment, the invention relates to a write-on sheetprotector, comprising: an envelope having an outer surface and an innersurface and being formed of a transparent coextruded sheet material; thesheet material comprising a water-absorbent film layer having a2-oxazoline polymer concentration of at least about 40% by weight, abase layer, the base layer having a first side and a second side, thewater-absorbent film layer overlying the first side of the base layer,and a skin layer overlying the second side of the base layer; the skinlayer forming the inner surface of the envelope; the water-absorbentfilm layer forming the outer surface of the envelope; the other surfaceof the envelope being an ink receptive surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the annexed drawing, like references indicate like parts orfeatures.

[0013]FIG. 1 is a schematic illustration of the side view of awater-absorbent film construction embodying the present invention in aparticular form.

[0014]FIG. 2 is a schematic illustration of the side view of analternative embodiment of the water-absorbent film construction of thepresent invention.

[0015]FIG. 3 is a schematic illustration of the side view of stillanother embodiment of the water-absorbent film construction of thepresent invention.

[0016]FIG. 4 is a schematic illustration of the side view of stillanother embodiment of the water-absorbent film construction of thepresent invention.

[0017]FIG. 5 is a schematic illustration of the side view of stillanother embodiment of the water-absorbent film construction of thepresent invention.

[0018]FIG. 6 is a schematic illustration of the side view of stillanother embodiment of the water-absorbent film construction of thepresent invention.

[0019]FIG. 7 is a plan view of a write-on sheet protector embodying thepresent invention in a particular form.

[0020]FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The inventive water-absorbent film constructions arecharacterized by a water-absorbent film layer overlying at least oneside of a base layer. The water absorbent film layer has a 2-oxazolinepolymer concentration of at least about 40% by weight. These filmconstructions have a number of utilities. For example, in oneembodiment, the water-absorbent film layer functions as an ink receptivelayer. This permits use of the inventive film construction in makinglabels, label stocks, and the like. It also permits use of the inventivefilm constructions in ink jet printing applications. In one embodiment,the inventive film construction is useful in making a transparent filmsheet protector that is capable of receiving written information on itsexterior surface. This is depicted in FIGS. 7 and 8 and is discussed ingreater detail below. In one embodiment, the invention relates to filmconstructions having non-skid or non-slip surfaces. In one embodiment,the invention relates to film constructions with water-absorbinganti-static surfaces, and film constructions with adhesive layers forlaminating the base layer to a paper substrate. In one embodiment, theinvention relates to film constructions that are useful as anti-fogfilms. Other uses include wash away labels, moisture indicators (e.g.,for disposable packages, diapers, etc.), security labels, and the like.

[0022] An advantage of the invention is that by combining thewater-absorbent film layer with the base layer, the inventive filmconstructions take advantage of the desirable properties provided by the2-oxazoline polymer in the water-absorbent film layer, and yet exhibitthe necessary mechanical and physical properties provided by the baselayer. This results in film constructions that are practical to use.

[0023] The term “water-absorbent film layer” refers to a film layer thatcan absorb water to the extent of at least about 0.1% by weight of itsweight at 20° C. In one embodiment, the water-absorbent film layer mayabsorb from about 0.1 to about 35% by weight of its weight, and in oneembodiment about 0.1 to about 20% by weight of its weight, and in oneembodiment about 0.1 to about 10% by weight of its weight, and in oneembodiment about 0.1 to about 5% by weight of its weight, and in oneembodiment about 0.1 to about 2% by weight of its weight, and in oneembodiment about 0.1 to about 1.5% by weight of its weight, and in oneembodiment about 0.1 to about 1% by weight of its weight, and in oneembodiment about 0.25 to about 0.5% by weight of its weight at 20° C.

[0024] The term “water-soluble polymer” refers to a polymer that issoluble in water to the extent of at least about 1 gram of polymer perliter of water at 20° C., and in one embodiment at least about 10 gramsof polymer per liter of water, and in one embodiment at least about 100grams of polymer per liter of water at 20° C.

[0025] The term “water-insoluble polymer” refers to a polymer that isnot a water-soluble polymer as defined above.

[0026] The term “overlies” and cognate terms such as “overlying” and thelike, when referring to the relationship of one or a first film layerrelative to another or a second film layer, refers to the fact that thefirst layer partially or completely lies over the second layer. Thefirst layer overlying the second layer may or may not be in contact withthe second layer. For example, one or more additional layers may bepositioned between the first layer and the second layer.

[0027] The inventive water-absorbent film construction, which isdepicted in one of its illustrated embodiments in FIG. 1, is generallyindicated by the reference numeral 10, and is comprised ofwater-absorbent film layer 12 which overlies a base layer 14. The baselayer 14 has a first side 14 a and a second side 14 b.

[0028] The water-absorbent film construction 10A depicted in FIG. 2 isidentical to the film construction 10 depicted in FIG. 1 except that thefilm construction 10A includes skin layer 16 which overlies the secondside 14 b of base layer 14.

[0029] The water-absorbent film construction 10B depicted in FIG. 3 isidentical to the film construction 10 depicted in FIG. 1 except thatfilm construction 10B includes tie layer 18 which is positioned betweenthe water-absorbent film layer 12 and the first side 14 a of base layer14. Tie layer 18 may be comprised of one or more layers of an adhesiveresin.

[0030] The water-absorbent film construction 10C depicted in FIG. 4 isidentical to the film construction 10B depicted in FIG. 3 except thatfilm construction 10C includes skin layer 16 which overlies the secondside 14 b of base layer 14.

[0031] The water-absorbent film construction 10D depicted in FIG. 5 isidentical to the film construction 10A depicted in FIG. 2 except thatfilm construction 10D includes adhesive layer 20 which overlies skinlayer 16.

[0032] The water-absorbent film construction 10E depicted in FIG. 6 isidentical to the film construction 10D depicted in FIG. 5 except thatfilm construction 10E includes tie layer 18 which is positioned betweenthe water-absorbent film layer 12 and the first side 14 a of base layer14. This film construction also includes a release liner 22 whichoverlies adhesive layer 20. In this embodiment, adhesive layer 20 is apressure sensitive adhesive layer. The release liner 20 is comprised ofbacking liner 24 and a release coating 26 applied to surface 24 a ofbacking liner 24. The release coating 26 is preferentially adhered tobacking liner 24 such that when the release liner 22 is separated fromthe adhesive layer 20, the release coating 26 remains adhered to thebacking liner 24.

[0033] The water-absorbent film layer 12 may have a thickness of about0.1 to about 2 mils, and in one embodiment about 0.25 to about 1 mil.The base layer 14 may have a thickness of about 1 to about 10 mils, andin one embodiment about 2 to about 5 mils. The skin layer 16 may have athickness of about 0.1 to about 2 mils, and in one embodiment about 0.25to about 1 mil.

[0034] The 2-oxazoline polymers used in the water-absorbent film layer12 are polymers containing repeating units represented by the formula:

[0035] These polymers may be prepared by a ring opening polymerizationof 2-oxazoline monomers represented by the formula:

[0036] In formulae (I) and (II), R is hydrogen or an alkyl group of 1 toabout 4 carbon atoms. R¹ is hydrogen, a phenyl group or an alkyl groupof 1 to about 4 carbon atoms. x is 1 or 2. In one embodiment, x is 1,each R is hydrogen and R¹ is an alkyl group of 1 to about 4 carbonatoms. In one embodiment, the 2-oxazoline monomer is2-ethyl-2-oxazoline. In one embodiment, the 2-oxazoline polymer ispoly(2-ethyl-2-oxazoline).

[0037] The ring-opening polymerization of the 2-oxazoline monomers maybe conducted in the presence of a cationic polymerization catalyst at areaction temperature of about 0° C.-200° C. The catalyst may be a strongmineral acid, an organic sulfonic acid or an ester thereof, an acidicsalt such as ammonium sulfate, a Lewis acid such as aluminumtrichloride, stannous tetrachloride, boron trifluoride, a organicdiazonium fluoroborate, a dialkyl sulfate, and the like.

[0038] The polymer obtained in the polymerization of the 2-oxazolinemonomers may be a linear, N-acylated polyalkyleneimine having amolecular structure containing repeating units represented by formula(I). A portion of the N-acyl groups may be hydrolyzed.

[0039] The term “2-oxazoline” is used herein to describe compoundshaving the structure defined by formula (II), including compoundswherein x is 2. R and R¹ may be inertly substituted. The term “inertlysubstituted” means that the moiety referred to contains no substituentgroup which interferes with the polymerization of the 2-oxazoline.Illustrative inert substituents include alkyl, alkenyl, alkoxy and thelike. Exemplary R groups include hydrogen, methyl, ethyl, propy, and thelike. Exemplary R¹ groups include hydrogen, methyl, ethyl, propyl,pentyl, cyclohexyl, and the like.

[0040] The 2-oxazoline polymer is water soluble and may have a molecularweight in the range of about 50,000 to about 1,000,000, and in oneembodiment about 100,000 to about 800,000, and in one embodiment about300,000 to about 700,000, and in one embodiment about 500,000. Themolecular weight may be determined by gel permeation chromatography.These polymers may have a kinematic viscosity in the range of about 18to about 100 cSt, and in one embodiment about 18 to about 24 cSt, and inone embodiment about 60 to about 80 cSt. These polymers may have apoly-dispersity in the range of about 3 to about 4.

[0041] Included among the commercially available 2-oxazoline polymersthat may be used are the poly(2-ethyl-2-oxazoline) polymers availablefrom Polymer Chemistry Innovations, Inc. under the tradename Aquazol.The products that may be used include those identified as follows:Target Molecular Poly-Dispersity Kinematic Viscosity Product WeightRange Range Aquazol 200 300,000 3-4 18-24 cSt Aquazol 500 500,000 3-460-80 cSt

[0042] The 2-oxazoline polymer may be blended with one or moreadditional water-soluble polymers. These additional water-solublepolymers include polyvinyl alcohol, polyvinyl pyrrolidone,polyacrylic-acid, polymethyl methacrylate, polymethyl methacrylic-acid,styrene maleic anhydride, methyl cellulose, ethyl cellulose,carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene oxide,polyethylene-imine, and mixtures thereof.

[0043] The 2-oxazoline polymer may be blended with one or morewater-insoluble polymers. The water-insoluble polymers that are usefulinclude polyolefins such as polyethylene, polypropylene, polybutylene,polystyrene, and the like. These water-insoluble polymers are eithercompatible with the 2-oxazoline polymer and, if used, the water-solublepolymer, or can be rendered compatible with the 2-oxazoline polymer andwater-soluble polymer by blending the polymers with a suitablecompatibilizing agent.

[0044] Compatibilizing agents that may be used include anhydridemodified polyolefins such as anhydride modified polypropylene; anhydridemodified polyethylene; anhydride-modified ethylene vinyl acetate;anhydride modified ethylmethyl acrylate; anhydride modified ethyleneethyl acrylate; anhydride modified ethyl acrylic acid; anhydridemodified ethyl glycidyl methacrylate; anhydride modified ethyl, n-butylacrylate; and copolymers, terpolymers and mixtures thereof. Usefulanhydride modified polyolefins include the anhydride modified ethylenevinyl acetates available from DuPont under the tradename Bynel®.

[0045] The concentration of the 2-oxazoline polymer in thewater-absorbent film layer 12 may range from about 40% to about 100% byweight, and in one embodiment about 50% to about 95% by weight, and inone embodiment about 60% to about 90% by weight, and in one embodimentabout 65% to about 75% by weight. The concentration of the additionalwater-soluble polymer may range up to about 30% by weight, and in oneembodiment up to about 20% by weight, and in one embodiment up to about10% by weight. The concentration of the water-insoluble polymer mayrange up to about 60% by weight, and in one embodiment from about 5% toabout 50% by weight, and in one embodiment about 10% to about 40% byweight, and in one embodiment about 25% to about 35% by weight. Theconcentration of the compatibilizing agent may range up to about 40% byweight, and in one embodiment from about 5% to about 30% by weight, andin one embodiment from about 10% to about 20% by weight.

[0046] The water-absorbent film layer 12 may further comprise one ormore cationic modifiers, wetting agents, colloidal silica, inherentlydissipative polymers, water proofing agents, anti-static agents, ormixtures of two or more thereof. Each of these may be present at aconcentration of up to about 10% by weight, and in one embodiment up toabout 5% by weight.

[0047] The base layer 14 may be comprised of metal foil, polymer film,paper sheet, or combinations thereof. The base layer 14 may be comprisedof textile including woven and non-woven fabrics made of natural orsynthetic fibers. The base layer 14 may be a single-layered constructionor it may be a multi-layered construction. These include polymeric filmsand multi-layered polymeric films. The multi-layered constructions havetwo or more layers, and in one embodiment about two to about ninelayers, and in one embodiment about two to about seven layers, and inone embodiment about three to about five layers. The layers of suchmulti-layered constructions may have the same composition and/or size orthey may be different.

[0048] The metal foils include foils of such metals as copper, gold,silver, tin, chromium, zinc, nickel, platinum, palladium, iron,aluminum, steel, lead, brass, bronze, and alloys of the foregoingmetals. Examples of such alloys include copper/zinc, copper/silver,copper/tin/zinc, copper/phosphorus, chromium/molybdenum,nickel/chromium, nickel/phosphorous, and the like. The metal foils canbe used by themselves or they can be joined or adhered to a polymericsheet or film to form a multi-layered laminate or construction.

[0049] The polymer films include polyolefins (linear or branched),polyamides, polystyrenes, nylon, polyesters, polyester copolymers,polyurethanes, polysulfones, styrene-maleic anhydride copolymers,styrene-acrylonitrile copolymers, ionomers based on sodium or zinc saltsof ethylene methacrylic acid, polymethyl methacrylates, cellulosics,acrylic polymers and copolymers, polycarbonates, polyacrylonitriles, andethylene-vinyl acetate copolymers. Included in this group are theacrylates such as ethylene methacrylic acid, ethylene methyl acrylate,ethylene acrylic acid and ethylene ethyl acrylate. Also, included inthis group are polymers and copolymers of olefin monomers having, forexample, 2 to about 12 carbon atoms, and in one embodiment 2 to about 8carbon atoms. These include the polymers of ac-olefins having from 2 toabout 4 carbon atoms per molecule. These include polyethylene,polypropylene, poly-1-butene, etc. An example of a copolymer within theabove definition is a copolymer of ethylene with 1-butene having fromabout 1 to about 10 weight percent of the 1-butene comonomerincorporated into the copolymer molecule. The polyethylenes that areuseful have various densities including low, medium and high densityranges. The low density range is from about 0.910 to about 0.925 g/cm³;the medium density range is from about 0.925 to about 0.940 g/cm³; andthe high density range is from about 0.940 to about 0.965 g/cm³. Anexample of a commercially available material that is useful is availablefrom Du Pont under the trade designation Mylar LB; this material isidentified as being a biaxially oriented polyester film. Films preparedfrom blends of copolymers or blends of copolymers with homopolymers alsoare useful. The films may be extruded as monolayered films ormulti-layered films. The films may be oriented films or nonorientedfilms.

[0050] The paper sheets include paper, clay coated paper, glassine,paperboard from straw, bark, wood, cotton, flax, cornstalks, sugarcane,bagasse, bamboo, hemp, and similar cellulose materials prepared by suchprocesses as the soda, sulfite or sulfate (Kraft) processes, the neutralsulfide cooking process, alkali-chlorine processes, nitric acidprocesses, semi-chemical processes, etc. Although paper of any basisweight can be employed, paper having basis weights in the range of fromabout 20 to about 150 pounds per ream (lb/ream) are useful, and papershaving weights in the range of from about 30 to about 60 lb/ream can beused.

[0051] The base layer 14 may be comprised of a polymer-coated paperwhich is basically a sheet of paper that is coated on either one or bothsides with a polymer coating. The polymer coating, which may becomprised of a high, medium, or low density polyethylene, polypropylene,polyester, and other similar polymer films, is coated on the papersurface to add strength and/or dimensional stability. The weight ofthese types of coated paper facestocks can vary over a wide range withweights in the range of about 5 to about 50 lb/ream being useful. Intotal, the final coated paper facestock may be comprised of betweenabout 10% and about 40% by weight polymer. For two-sided coatings, thequantity of polymer is usually approximately evenly divided between thetop and bottom surface of the paper.

[0052] The skin layer 16 may be made from any heat-activatable adhesivematerial, thermoplastic film-forming material, or mixture thereof. Theheat-activatable adhesive materials may be polymers (e.g., homopolymers,copolymers, terpolymers, etc.) containing carbonyl or hydroxyl groups ora combination thereof. These polymers are non-tacky to the touch untilactivated by the application of heat at which time they become tacky tothe touch. The term “non-tacky to the touch” refers to an adhesive thatwhen cast as a film and dried does not feel sticky or tacky at roomtemperature (about 20° C.) and normal relative humidity (less than about25% RH). The heat-activatable adhesives that can be used includepolyamides such as nylon, polyester copolymers, ionomers based on sodiumor zinc salts of ethylene methacrylic acid, polyacrylonitriles,ethylene-vinyl acetate copolymers, and mixtures of two or more thereof.Included in this group are acrylate copolymers such as ethylenemethacrylic acid, ethylene methyl acrylate, ethylene acrylic acid,ethylene ethyl acrylate, and the like. The ethylene methyl acrylatecopolymers available from Chevron under the tradename EMAC can be used.TC 120, a product available from ExxonMobil identified as an ethylenemethyl acrylate copolymer, can be used. USEP 307, a product availablefrom Equistar identified as an ethylene vinyl acetate copolymer, can beused.

[0053] The thermoplastic film-forming material may be any thermoplasticfilm-forming material known in the art. These include linear or branchedpolyolefins. The polyolefins may be amorphous polyolefins. Thepolyolefins include polymers and copolymers of olefin monomers having 2to about 12 carbon atoms, and in one embodiment 2 to about 8 carbonatoms, and in one embodiment 2 to about 4 carbon atoms. These includethe polymers of alpha-olefins. The polyolefins include polyethylene,polypropylene, poly-1-butene, etc. The polyethylenes that are usefulhave various densities including low, medium and high density ranges asdefined above. Ethylene-propylene copolymers, including those availablefrom Dow under the trade designation DS6D81, can be used.

[0054] The base layer 14, when in the form of a polymer film, and theskin layer 16 may be transparent or pigmented. In one embodiment, one ofthese layers is transparent and the other is pigmented. In oneembodiment, neither of these layers contain pigment and both layers aretransparent. The pigments that can be used include titanium dioxide,both rutile and anatase crystal structure. In one embodiment, thepigment that is used is in the form of a concentrate containing thepigment and a resin carrier. The concentrate may contain, for example,about 20% to about 80% by weight pigment, and about 20% to about 80% byweight resin carrier. The resin carrier can be any thermoplastic polymerhaving a melting point in the range of about 100° C. to about 265° C.Examples include polyethylene, polypropylene, polybutylene, polyester,nylon and the like. In one embodiment, a titanium dioxide concentrate isused which is comprised of a blend of about 30% to about 70% by weightpolypropylene and about 70% to about 30% by weight titanium dioxide. Anexample of a commercially available pigment concentrate that can be usedis available from A. Schulman Inc. under the tradename PolyBatch WhiteP8555 SD, which is identified as a white color concentrate having acoated rutile titanium dioxide concentration of 50% by weight in apolypropylene homopolymer carrier resin. Another example is Ampacet110233 which is a product of Ampacet Corporation identified as a TiO₂concentrate containing 50% rutile TiO₂ and 50% low density polyethylene.The concentration of pigment in the base layer and/or skin layer 16 maybe up to about 25% by weight, and when used is generally in the range ofabout 5% to about 25% by weight, and in one embodiment about 10% toabout 20% by weight.

[0055] The base layer 14 and/or skin layer 16 may include a fillermaterial to increase opacity. The fillers that can be used includecalcium carbonate and talc. In one embodiment, the filler is added inthe form of a concentrate containing the filler and a resin carrier. Theconcentrate may contain, for example, about 20% to about 80% by weightfiller, and about 20% to about 80% by weight resin carrier. The resincarrier can be any thermoplastic polymer having a melting point in therange of about 100° C. to about 265° C. Examples include polyethylene,polypropylene, polybutylene, polyester, nylon, and the like. Alsoincluded are thermoplastic copolymers such as ethylene methylacrylate,and the like. In one embodiment, a calcium carbonate concentrate is usedwhich is comprised of a blend of about 50% to about 80% by weightpolypropylene and about 20% to about 50% by weight calcium carbonate. Anexample of a commercially available pigment concentrate that can be usedis available from A. Schulman Inc. under the tradename PF 920, which isidentified as a calcium carbonate concentrate having a calcium carbonateconcentration of 40% by weight in a polypropylene homopolymer carrierresin. Another example is Ampacet 101087 which is a product of AmpacetCorporation identified as a calcium carbonate concentrate containing 30%by weight calcium carbonate and 70% by weight ethylene methylacrylate.The concentration of filler in the base layer 14 and/or skin layer 16may be up to about 40% by weight, and when used is generally in therange of about 10% to about 40% by weigh, and in one embodiment about10% to about 35% by weight.

[0056] The base layer 14 and/or skin layer 16 may contain one or moreslip additives. These include primary amides such as stearamide,behenamide, oleamide, erucamide, and the like; secondary amides such asstearyl erucamide, erucyl erucamide, oleyl palmitamide, stearylstearamide, erucyl stearamide, and the like; ethylene bisamides such asN,N′-ethylenebisstearamide, N,N′-ethylenebisolemide and the like; andcombinations of any two or more of the foregoing amides. An example of auseful slip additive is available from A. Schulman under the trade Sper6; this product is identified as a concentrate containing 6% by weightof an unsaturated C₁₇ fatty acid amide dispersed in polypropylene. Theslip additive may be used at a concentration in the range of up to about4% by weight, and in one embodiment about 0.05% to about 2% by weight,and in one embodiment about 0.1% to about 0.5% by weight.

[0057] The base layer 14 and/or skin layer 16 may contain one or moreantiblock additives. These include natural silica, diatomaceous earth,synthetic silica, glass spheres, ceramic particles, calcium carbonateparticles, calcium silicate particles, fatty amide particles, aluminumsilicate, and the like. Examples of commercially available antiblockadditives include those available from A. Schulman under the tradedesignation Polybatch ABPP05SC which is identified as a concentratecontaining 5% by weight amorphous silica dispersed in anethylene-propylene copolymer. A. Schulman CABL 4040, which is in theform of solid pellets containing 5% silicate and 5% ceramic microsphereswith the remainder being a low density polyethylene carrier, can beused. Schulman AB5, which is an antiblock concentrate available from A.Schulman which comprises 5% solid synthetic amorphous silica in 95% lowdensity polyethylene, can also be used. Polybatch F-20, which isavailable from A. Schulman and is identified as concentrate containing20% natural silica based in low density polyethylene, can be used. Otheruseful additives include those available from Zeelan Industries underthe trade designation Zeeospheres; 3M under the trade designationScotchlite Glass Bubbles; Potters Industries under the trade designationSpheriglass; Mo-Sci Corporation under the trade designation PrecisionGlass Spheres (Class IV); Huber under the trade designation Huber Q;Nyco Minerals under the trade designations Nycor, Nyad, Ultrafibe,Primglos, Nyglos and Wallastocoat; Jayco under the trade designationDragonite; Witco under the trade designation Kenamide; and U.S. Silicaunder the trade designation Min-U-Sil. The antiblock additive may beused at a concentration of up to about 20% by weight, and in oneembodiment about 0.1% to about 10% by weight, and in one embodimentabout 0.5% to about 5% by weight.

[0058] The antiblock and slip additives may be added together in theform of a resin concentrate. An example of such a concentrate isavailable from DuPont under the tradename Elvax CE9619-1. This resinconcentrate contains 20% by weight silica, 7% by weight of an amide slipadditive, and 73% by weight of Elvax 3170 (a product of DuPontidentified as an ethylene/vinyl acetate copolymer having a vinyl acetatecontent of 18% by weight). The amount of antiblock and slip additivesmay be the same or different in each layer. Generally it is desireableto minimize the amount of these additives to avoid ink adhesion and lowheat seal bond problems. However, a sufficient amount to preventblocking of self wound rolls of film is usually desirable.

[0059] The base layer 14 and/or skin layer 16 may contain a minor amountof an adhesive resin to enhance the adhesion of the base layer 14 andskin layer 16 to each other. The adhesive resin in the base layer 14 canalso be used to enhance the adhesion of the base layer 14 to thewater-absorbent film layer 12. The adhesive resin may be anethylene/vinyl acetate copolymer. These include DuPont Elvax 3170 and3190LG. The adhesive resins available from DuPont under the tradenameBynel may be used. The adhesive resin may be used at a concentration ofup to about 100% by weight, and in one embodiment about 45% to about 85%by weight of the base layer 14 and/or skin layer 16. Also, oralternatively, a tie layer may be positioned between the base layer 14and skin layer 16. Also, tie layer 18 may be positioned between the baselayer 14 and the water-absorbent film layer 12. The tie layers are usedto enhance the adhesion of the skin layer 16 and/or the water-absorbentfilm layer 12 to the base layer 14. The tie layers may be comprised ofone of the above mentioned adhesive resins, or one or more of theheat-activatable activatable adhesive materials discussed above as beinguseful in making the skin layer 16. The tie layers may be comprised ofone of the mixtures of heat-activatable adhesive materials andfilm-forming thermoplastic materials described above as being useful informing the skin layer 16. Each tie layer may have a thickness of about5% to about 40% of the thickness of the base layer 14, and in oneembodiment about 10% to about 25%.

[0060] The base layer 14 and/or skin layer 16 may contain ultraviolet(UV) light absorbers or other light stabilizers. These additives areincluded to prevent degradation due to sunlight. These additives includehindered amine light stabilizers such as those described in U.S. Pat.No. 4,721,531, which is incorporated herein by reference. The hinderedamine light stabilizers include derivatives of 2,2,6,6-tetraalkylpiperidines or substituted piperizinediones.

[0061] Hindered amine light stabilizers that are useful are availablecommercially from Ciba-Geigy Corporation under the trade designations“Tinuvin” and “Chemassorb”, and from Cytec under the general designation“Cyasorb-UV.” UV light absorbers that are useful include those availablefrom Ciba-Geigy under the “Tinuvin” name and Great Lakes ChemicalCorporation under the trade designation “Lowilite.” The concentration ofUV absorber or light stabilizer may be up to about 1% by weight, and inone embodiment about 0.1% to about 0.5% by weight.

[0062] The water-absorbent film layer 12 and base layer 14 may be formedby simultaneous coextrusion from two or more extruders and a suitablecoextrusion die whereby the water-absorbent film layer 12 and base layer14 are adhered to each other in a permanently combined state to providea unitary coextrudate.

[0063] As indicated above, skin layer 16 and one or more tie layers ofan adhesive resin, including tie layer 18, may be used. These layers maybe coextruded with the water-absorbent film layer 12 and base layer 14.Alternatively, coating processes known in the art may be used to laydown the base layer 14 as well as the other layers mentioned above ontoa moving web. Also, when the base layer 14 is not a polymeric film, thewater-absorbent film layer, and other layers, can be applied usingcoating processes known in the art. The coating processes includegravure, reverse gravure, offset gravure, roller coating, brushing,knife-over roll, metering rod, reverse roll coating, doctor knife,dipping, die coating, curtain coatings, spraying, and the like.

[0064] The adhesive layer 20 may be comprised of any adhesive known inthe art for making film constructions, including tapes, labels, and thelike. The adhesive layer 20 may be comprised of a moisture-activatableadhesive or a pressure sensitive adhesive. These adhesives may be coatedon to the inventive water-absorbent film construction using knowntechniques. The adhesive layer may have a thickness of about 0.1 toabout 2 mils, and in one embodiment about 0.25 to about 1 mil.

[0065] The moisture-activatable adhesives are non-tacky to the touchuntil activated. Once activated, by contact with moisture, they becomepressure sensitive adhesives. The moisture-activatable adhesives includeacrylic adhesives which are known in the art. In one embodiment, thisadhesive may be a polymer derived from a monomer mixture comprisingalkyl acrylates wherein the alkyl group contains about 4 to about 8carbon atoms, methyl acrylate, vinyl acetate, and methacrylic acid oracrylic acid. These adhesives are described in U.S. Pat. No. 6,124,417,which is incorporated herein by reference.

[0066] The pressure-sensitive adhesive can be any pressure sensitiveadhesive known in the art. These adhesives are tacky to the touch. Thepressure-sensitive adhesives include rubber based adhesives, acrylicadhesives, vinyl ether adhesives, silicone adhesives, and mixtures oftwo or more thereof. These adhesives may be hot melt, solvent-based orwater based adhesives. The pressure sensitive adhesives may contain as amajor constituent an adhesive polymer such as acrylic-type polymers;block copolymers; natural, reclaimed, or styrene-butadiene rubbers;tackified natural or synthetic rubbers; or random copolymers of ethyleneand vinyl acetate, ethylene-vinyl-acrylic terpolymers, polyisobutylene,poly (vinyl ether), etc. Other materials may be included in the pressuresensitive adhesive such as tackifying resins, plasticizers,antioxidants, fillers, pigments, waxes, etc.

[0067] The release liner 22 is comprised of a backing liner 24 and alayer of a cured release coating 26 adhered to side 24 a of backingliner 24. The release coating 26 is in contact with the adhesive layer20 when the release liner 22 is adhered to the inventive water-absorbentconstruction. The release coating 26 can be made using any releasecoating composition known in the art. Silicone release coatingcompositions are useful. The silicone release coating compositions aretypically comprised of polyorganosiloxanes and, more often,polydimethylsiloxanes. The silicone release coating composition may beroom temperature cured, thermally cured, or radiation cured. Generally,the room temperature and thermally curable compositions contain at leastone polyorganosiloxane and at least one catalyst (or curing agent) forthe polyorganosiloxane. These compositions may also contain at least onecure accelerator and/or adhesion promoter (sometimes referred to as ananchorage additive). As is known in the art, some materials have thecapability of performing both functions, i.e., the capability of actingas a cure accelerator to increase the rate, reduce the curingtemperature, etc., and also as an adhesion promoter to improve bondingof the silicone composition to the substrate.

[0068] The backing liner 24 may comprise paper, polymer film, or acombination thereof. Any of the paper, polymer films, or combinationsthereof, discussed above as being useful as the base layer 14 can beused as the backing liner 24. Paper liners are particularly usefulbecause of the wide variety of applications in which they can beemployed. Paper is also relatively inexpensive and has desirableproperties such as antiblocking, antistatic, dimensional stability, andcan potentially be recycled. Any type of paper having sufficient tensilestrength to be handled in conventional paper coating and treatingapparatus can be employed as the liner. Although paper of any weight canbe employed as the liner material, paper having a basis weight in therange of about 30 to about 120 lb/ream may be used, and papers having abasis weight in the range of about 60 to about 100 lb/ream may be used.

[0069] The release coating 26 may be applied to the backing liner 24 andcured using known techniques. The application techniques includegravure, reverse gravure, offset gravure, roller coating, brushing,knife-over roll, metering rod, reverse roll coating, doctor knife,dipping, die coating, spraying, curtain coating, and the like. The coatweight of the release coating 26 may be in the range of about 0.1 gramsper square meter (gsm) to about 10 gsm or more, and in one embodimentabout 0.3 gsm to about 2 gsm. The thickness of the release liner 22 mayrange from about 4 mils to about 10 mils, and in one embodiment fromabout 4 mils to about 6 mils.

[0070] In the following examples, as well as throughout thespecification and claims, unless otherwise indicated, all parts andpercentages are by weight.

Example 1

[0071] A water-absorbent film construction corresponding to filmconstruction 10A in FIG. 2 is coextruded. The overall thickness of thefilm construction is 3.2 mils. The composition and thickness of each ofthe layers is as follows: Water-absorbent film layer 12 (0.46 mil):Aquazol 500 (product of Polymer Chemistry 70.0% Innovations, Inc.identified as poly (2- ethyl-2-oxazoline) having a molecular weight of500,000, a polydispersity in the range of 3-4, and a kinematic viscosityof 60-80 cSt) Bynel CXA 2002 (product of DuPont identified 15.0% asanhydride modified ethylene vinyl acetate adhesive resin) DS6D81(product of Dow identified as 14.0% ethylene-propylene copolymer)Polybatch ABPPO5SC (product of A.   1% Schulman Inc. identified as aconcentrate containing 5% amorphous silica dispersed in anethylene-propylene copolymer) Base Layer 14 (2.28 mil) 5A97 (product ofDow identified as a polypropylene  100% homopolymer) Skin Layer 16 (0.46mil) DS6D81 91.5% Sper 6 (product of A. Schulman Inc.  4.5% identifiedas a concentrate containing 6% of an unsaturated C₁₇ fatty acid amidedispersed in polypropylene) Polybatch ABPPO5SC  4.0%

[0072] This film construction is useful as an ink receptive filmconstruction, the ink receptive layer being the water-absorbent filmlayer 12. This film construction may be used to make the writabledocument protector assembly 110 depicted in FIGS. 7 and 8.

Example 2

[0073] A water-absorbent film construction corresponding to filmconstruction 10B in FIG. 3 is coextruded. This film is useful as a waterabsorbing anti-static surface film for non-pressure sensitive adhesiveapplications. It is also useful as a non-skid or non-slip printable filmfor use with floor tile. This film can be used as an adhesive for usewith paper laminates. The overall thickness of the film construction is3.00 mils. The composition and thickness of each layer is as follows:Water-absorbent film layer 12 (0.30 mil) Aquazol 500 75.0% TC120(product of ExxonMobil identified 24.0% as an ethylene methyl acrylatecopolymer) Polybatch ABPPO5SC  1.0% Tie layer 18 (0.30 mil): TC120 50.0%5A97 50.0% Base layer 14 (2.40 mil): 5A97 95.0% Polybatch ABPFO5SC  2.5%Sper 6  2.5%

Example 3

[0074] A water-absorbent film construction corresponding to filmconstruction 110C in FIG. 4 is coextruded. This film is useful as awater absorbing anti-static surface film for pressure sensitive adhesiveapplications. It is useful as a non-skid or non-slip printable film forfloor tile. This film can also be used as an adhesive for use with paperlaminates. The overall thickness of the film construction is 3.00 mils.The composition and thickness of each layer is as follows:Water-absorbent film layer 12 (0.30 mil) Aquazol 500 75.0% TC120 24.0%Polybatch ABPPO5SC 1.0% Tie layer 18 (0.30 mil): TC120 50.0% 5A97 50.0%Base layer 14 (2.10 mil): 5A97 70.0% TC120 30.0% Skin layer 16 (0.30mil) 5A97 50.0% TC120 50.0%

Example 4

[0075] A water-absorbent film construction corresponding to filmconstruction 10 in FIG. 1 is coextruded. This film is useful as a waterabsorbing anti-static surface film for non-pressure sensitive adhesiveapplications. The overall thickness of the film construction is 2.70mils. The composition and thickness of each layer is as follows:Water-absorbent film layer 12 (0.30 mil) Aquazol 500 75.0% TC120 24.0%Polybatch ABPPO5SC 1.0% Base layer 14 (2.40 mil): 5A97 70.0% TC120 25.0%Polybatch ABPFO5SC 2.5% Sper 6 2.5%

Example 5

[0076] A water-absorbent film construction corresponding to filmconstruction 10A in FIG. 2 is coextruded. This film is useful as a waterabsorbing anti-static surface film for pressure sensitive adhesiveapplications. The overall thickness of the film construction is 3.00mils. The composition and thickness of each layer is as follows:Water-absorbent film layer 12 (0.30 mil) Aquazol 500 75.0% TC120 24.0%Polybatch ABPPO5SC 1.0% Base layer 14 (2.40 mil): 5A97 70.0% TC120 25.0%Polybatch ABPFO5SC 2.5% Sper 6 2.5% Skin layer 16 (0.30 mil): 5A97 50.0%TC120 50.0%

Example 6

[0077] A water-absorbent film construction corresponding to filmconstruction 10B in FIG. 3 is coextruded. This film is useful as anon-skid or non-slip printable film for use with floor tile whereinnon-pressure sensitive adhesive applications are desired. The overallthickness of the film construction is 3.00 mils. The composition andthickness of each layer is as follows: Water-absorbent film layer 12(0.30 mil) Aquazol 500 60.0% TC120 24.0% CABL 4040 (product of A.Schulman identified 15.0% as solid pellets containing 5% silicate, 5%ceramic microspheres with the remainder being a low density polyethylenecarrier) Polybatch ABPPO5SC 1.0% Tie layer 18 (0.30 mil): TC120 50.0%5A97 50.0% Base layer 14 (2.40 mil): 5A97 95.0% Polybatch ABPFO5SC 2.5%Sper 6 2.5%

Example 7

[0078] A water-absorbent film construction corresponding to filmconstruction 10C in FIG. 4 is coextruded. This film is useful as anon-skid or non-slip printable film for floor tile wherein pressuresensitive adhesive applications are desired. The overall thickness ofthe film construction is 3.00 mils. The composition and thickness ofeach layer is as follows: Water-absorbent film layer 12 (0.30 mil)Aquazol 500 60.0% TC120 24.0% CABL 4040 15.0% Polybatch ABPPO5SC 1.0%Tie layer 18 (0.30 mil): TC120 50.0% 5A97 50.0% Base layer 14 (2.10mil): 5A97 70.0% TC120 30.0% Skin layer 16 (0.30 mil) 5A97 50.0% TC12050.0%

Example 8

[0079] A water-absorbent film construction corresponding to filmconstruction 10B in FIG. 3 is coextruded. This film is useful as anadhesive film for paper laiminates. The overall thickness of the filmconstruction is 3.00 mils. The composition and thickness of each layeris as follows: Water-absorbent film layer 12 (0.30 mil) Aquazol 50050.0% EVAL F101 (a product of Evalco identified as an ethylene vinylalcohol copolymer)   25% TC120 24.0% Polybatch ABPPO5SC  1.0% Tie layer18 (0.30 mil): TC120 50.0% 5A97 50.0% Base layer 14 (2.40 mil): 5A9795.0% Polybatch ABPFO5SC  2.5% Sper 6  2.5%

Example 9

[0080] A water-absorbent film construction corresponding to filmconstruction 10C in FIG. 4 is coextruded. This film is useful as anadhesive for pressure sensitive adhesive applications. The overallthickness of the film construction is 3.00 mils. The composition andthickness of each layer is as follows: Water-absorbent film layer 12(0.30 mil) Aquazol 500 50.0% EVAL F101 25.0% TC120 24.0% PolybatchABPPO5SC  1.0% Tie layer 18 (0.30 mil): TC120 50.0% 5A97 50.0% Baselayer 14 (2.10 mil): 5A97 70.0% TC120 30.0% Skin layer 16 (0.30 mil)5A97 50.0% TC120 50.0%

[0081] In one embodiment, the invention further comprises a write-onsheet protector, such as the write-on sheet protector 110 depicted inFIGS. 7 and 8, which is made using the inventive water-absorbent filmconstruction. The water-absorbent film constructions 10A and 10Cdepicted in FIGS. 2 and 4 are particularly suitable for this use. Whenforming the sheet protector 110 the water-absorbent film layer 12 formsthe outer surface of the sheet protector and functions as an inkreceptive substrate. The skin layer 16 forms the inner surface of thesheet protector. Referring to FIGS. 7 and 8, the write-on sheetprotector 110 includes an upper transparent plastic sheet 112 and alower transparent plastic sheet 114. These two sheets may be formed froma single sheet folded over at the outer edge 116, or alternatively canbe made of two overlying sheets. The sheet protector 110 is open at thetop edge, as shown in FIG. 7, and heat sealed along the lower edge 118.The sheet protector 110 is heat sealed along thermo-sealing lines 120and 122 with an extra reinforcing strip 124 mounted between thethermo-sealing lines 120 and 122. The reinforced left edge of the sheetprotector 110 may be provided with holes 126 for convenience in mountingthe sheet protector 110 into a ringed binder. Formed within the sheetprotector 110 is a pocket or envelope suitable for receiving a document(e.g., sheet of paper, photograph, letter, drawing, etc.).

[0082] The heat sealing may be accomplished by applying a heated die tothe double layer material. The heat sealing may be in the form of aseries of welds with spaces between the welds to allow for the easyinsertion of sheet material. Alternatively, instead of thermal bonding,the edges may be secured together in any desired manner, such as by highfrequency welding or by a thin line of permanent adhesive or by otherknown techniques.

[0083] In one embodiment, the sheet protector 110 is approximately 9inches in width and about 11-⅛ inches in its longer dimension. Thereinforcing strip 124 may be about ⅜ inch wide. The envelope or pocketformed within the sheet protector 110 is large enough to receive anunfolded sheet, 8½ inches by 11 inches in size.

[0084] Referring to FIG. 7, within the envelope or pocket formed withinthe sheet protector 110 is a letter 132 which is protected from damageby the sheet protector 110. Written on the outer surface of the sheetprotector 110 in ink are certain legends 134 calling attention tocertain passages or parts in the letter 132. Thus, by using the sheetprotector 110, written comments may be made on the outer surface of thesheet protector relative to the letter 132 without defacing the letteritself. Subsequently, if desired, the original letter 132 may bewithdrawn from the sheet protector 110. Instead of the letter 132, aphotograph, drawing or other document can be placed in the envelope.

[0085] While the invention has been explained in relation to itspreferred embodiments, it is to be understood that various modificationsthereof will become apparent to those skilled in the art upon readingthe specification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1. A water-absorbent film construction, comprising: a water-absorbentfilm layer overlying a base layer, the water-absorbent film layer beingcomprised of at least about 40% by weight of at least one 2-oxazolinepolymer.
 2. The film construction of claim 1 wherein the base layer hasa first side and a second side, the water-absorbent film layer overliesthe first side, and a skin layer overlies the second side.
 3. The filmconstruction of claim 1 wherein the film construction further comprisesa tie layer positioned between the water-absorbent film layer and thebase layer.
 4. The film construction of claim 1 wherein the base layerhas a first side and a second side, the water-absorbent film layeroverlies the first side, a tie layer is positioned between thewater-absorbent film layer and the base layer, and a skin layer overliesthe second side.
 5. The film construction of claim 1 wherein the baselayer has a first side and a second side, the water-absorbent film layeroverlies the first side, a skin layer overlies the second side, and anadhesive layer overlies the skin layer.
 6. The film construction ofclaim 5 wherein the adhesive layer is comprised of a pressure sensitiveadhesive, and a release liner overlies the pressure sensitive adhesive.7. The film construction of claim 6 wherein the release liner iscomprised of a release coating and a backing liner, the release coatingbeing positioned between the pressure sensitive adhesive and the backingliner.
 8. The film construction of claim 1 wherein the 2-oxazolinepolymer contains repeating units represented by the formula:

wherein: R is hydrogen or an alkyl group of 1 to about 4 carbon atoms;R¹ is hydrogen, a phenyl group or an alkyl group of 1 to about 4 carbonatoms; and x is 1 or
 2. 9. The film construction of claim 1 wherein the2-oxazoline polymer is poly(2-ethyl-2-oxazoline).
 10. The filmconstruction of claim 1 wherein the water-absorbent film layer furthercomprises at least one additional water-soluble polymer.
 11. The filmconstruction of claim 1 wherein the water-absorbent film layer furthercomprises at least one water-insoluble polymer.
 12. The filmconstruction of claim 1 wherein the water-absorbent film layer furthercomprises at least one compatibilizing agent.
 13. The film constructionof claim 1 wherein the base layer comprises a single-layeredconstruction.
 14. The film construction of claim 1 wherein the baselayer comprises a multi-layered construction.
 15. The film constructionof claim 1 wherein the base layer comprises foil, paper, polymer film,textile, or a combination thereof.
 16. The film construction of claim 1wherein the base layer is comprised of a polymeric film.
 17. The filmconstruction of claim 1 wherein the base layer is comprised of amulti-layered polymeric film.
 18. The film construction of claim 1wherein the water-absorbent film layer and the base layer are comprisedof a coextrudate.
 19. The film construction of claim 2 wherein the skinlayer is comprised of a heat-activatable adhesive material, athermoplastic film-forming material, or a mixture thereof.
 20. The filmconstruction of claim 19 wherein the heat-activatable adhesive is apolymer containing carbonyl groups, hydroxyl groups, or a combination ofcarbonyl and hydroxyl groups.
 21. The film construction of claim 19wherein the heat-activatable adhesive material is a polyamide, apolyester copolymer, an ionomer based on sodium or zinc salts ofethylene methacrylic acid, a polyacrylontrile, an ethylene vinyl acetatecopolymer, an ethylene methacrylic acid copolymer, an ethylenemethylacrylate copolymer, an ethylene acrylic acid copolymer, anethylene ethyl acrylate copolymer, or a mixture of two or more thereof.22. The film construction of claim 19 wherein the thermoplasticfilm-forming material is a polymer or copolymer of an olefin monomer.23. The film construction of claim 19 wherein the thermoplasticfilm-forming material is comprised of polypropylene or a copolymer ofethylene and propylene.
 24. The film construction of claim 2 wherein theskin layer is comprised of a mixture of polypropylene and ethylenemethylacrylate copolymer.
 25. The film construction of claim 3 whereinthe tie layer is comprised of a heat-activatable adhesive material, or amixture of a heat-activatable adhesive material and a thermoplasticfilm-forming material.
 26. The film construction of claim 25 wherein theheat-activatable adhesive material is a polymer containing carbonyl,hydroxyl groups, or a combination of carbonyl and hydroxyl groups. 27.The film construction of claim 25 wherein the heat-activatable adhesivematerial is a polyamide, a polyester copolymer, an ionomer based onsodium or zinc salts of ethylene methacrylic acid, a polyacrylontrile,an ethylene vinyl acetate copolymer, an ethylene methacrylic acidcopolymer, an ethylene methylacrylate copolymer, an ethylene acrylicacid copolymer, an ethylene ethyl acrylate copolymer, or a mixture oftwo or more thereof.
 28. The film construction of claim 25 wherein thethermoplastic film-forming material is a polymer or copolymer of anolefin monomer.
 29. The film construction of claim 25 wherein thethermoplastic film-forming material is comprised of polypropylene or acopolymer of ethylene and propylene.
 30. The film construction of claim3 wherein the tie layer is comprised of a mixture of polypropylene andethylene methylacrylate copolymer.
 31. A water-absorbent filmconstruction, comprising: a water-absorbent film layer having a2-oxazoline polymer concentration of at least about 40% by weight; abase layer, the base layer having a first side and a second side, thewater-absorbent film layer overlying the first side of the base layer;and a skin layer comprising at least one heat-activatable adhesivematerial overlying the second side of the base layer.
 32. The filmconstruction of claim 31 wherein the film construction further comprisesa tie layer positioned between the water-absorbent film layer and thebase layer.
 33. The film construction of claim 31 wherein the2-oxazoline polymer contains repeating units represented by the formula:

wherein: R is hydrogen or an alkyl group of 1 to about 4 carbon atoms;R¹ is hydrogen, a phenyl group or an alkyl group of 1 to about 4 carbonatoms; and x is 1 or
 2. 34. The film construction of claim 31 whereinthe 2-oxazoline polymer is poly(2-ethyl-2-oxazoline).
 35. The filmconstruction of claim 31 wherein the water-absorbent film layer furthercomprises at least one additional water-soluble polymer.
 36. The filmconstruction of claim 31 wherein the water-absorbent film layer furthercomprises at least one water-insoluble polymer.
 37. The filmconstruction of claim 31 wherein the water-absorbent film layer furthercomprises at least one compatibilizing agent.
 38. The film constructionof claim 31 wherein the base layer comprises a single-layeredconstruction.
 39. The film construction of claim 31 wherein the baselayer comprises a multi-layered construction.
 40. The film constructionof claim 31 wherein the base layer comprises foil, paper, polymer film,textile, or a combination thereof.
 41. The film construction of claim 31wherein the base layer is comprised of a polymeric film.
 42. The filmconstruction of claim 31 wherein the base layer is comprised of amulti-layered polymeric film.
 43. The film construction of claim 31wherein the water-absorbent film layer and the base layer are comprisedof a coextrudate.
 44. The film construction of claim 31 wherein theheat-activatable adhesive is a polymer containing carbonyl groups,hydroxyl groups, or a combination of carbonyl and hydroxyl groups. 45.The film construction of claim 31 wherein the heat-activatable adhesivematerial is a polyamide, a polyester copolymer, an ionomer based onsodium or zinc salts of ethylene methacrylic acid, a polyacrylontrile,an ethylene vinyl acetate copolymer, an ethylene methacrylic acidcopolymer, an ethylene methylacrylate copolymer, an ethylene acrylicacid copolymer, an ethylene ethyl acrylate copolymer, or a mixture oftwo or more thereof.
 46. The film construction of claim 31 wherein theskin layer further comprises a thermoplastic film-forming material. 47.A write-on sheet protector, comprising: an envelope having an outersurface and an inner surface and being formed of a transparentcoextruded sheet material; the sheet material comprising awater-absorbent film layer having a 2-oxazoline polymer concentration ofat least about 40% by weight, a base layer, the base layer having afirst side and a second side, the water-absorbent film layer overlyingthe first side of the base layer, and a skin layer overlying the secondside of the base layer; the skin layer forming the inner surface of theenvelope; the water-absorbent film layer forming the outer surface ofthe envelope; the outer surface of the envelope being an ink receptivesurface.
 48. The sheet protector of claim 47 wherein the envelope isformed from one sheet of the sheet material, the sheet material beingfolded over to form one sealed edge of the envelope, the sheet materialbeing sealed along two additional edges of the envelope, one edge of theenvelope being open.
 49. The sheet material of claim 47 wherein theenvelope is formed from two overlying sheets of the sheet material, thetwo sheets of sheet material being sealed along three edges to form theenvelope, one edge of the envelope being open.
 50. The sheet protectorof claim 47 wherein the envelope has three sealed edges and the sheetprotector further comprises a reinforcing strip mounted on one of thesealed edges.
 51. The sheet protector of claim 50 wherein the sheetprotector further comprises one or more holes in the reinforcing stripfor mounting the sheet protector in a ringed binder.